A lipid biomarker investigation of the sources and distribution of organic matter in river-influenced shelf sediments of NE Brazil

摘要

A better understanding of the sources - continental or marine - and distribution of organic matter (OM) in shelf sediments of areas under distinct natural and anthropogenic forces is essential to obtain a global view of the carbon cycle. In this study, we evaluated the influence of river discharge on the OM accumulation pattern in a portion of the NE Brazilian continental margin (10-15 degrees S) by considering a suite of lipid biomarkers (sterols, n-alcohols, phytol and taraxerol) in surface sediments. A total of 36 samples were collected adjacent to river mouths representing drainage basins of varying size and representing different human intervention levels, namely the Sao Francisco, Vaza Barris, Sergipe and Piaui-Real rivers. The average concentration of the total quantified lipids was 3.77 +/- 1.93 mu g g(-1), with the lowest values detected at the Sao Francisco River pro-delta. This result seems to reflect the reductions in the Sao Francisco river flow during the last decades caused by human interventions (diverse water use and urbanization, among others) and climate change (reduced precipitation) along its drainage basin, which seems to affect other smaller basins to a lesser extent. Our findings highlight that human interventions and climate change are relevant drivers for biogeochemical processes even in shelves receiving the flow from small to medium rivers in Brazil, which agree with other records worldwide. Finally, we hope the data presented herein contribute to the development of a management system based on a watershed-coastal ocean scaling and socio-environmental perspective for the Sergipe and Alagoas shelf. (C) 2020 Elsevier Ltd. All rights reserved.